Did you know that some birds lay blue eggs? For example, blackbirds, starlings and the American robin. But why has evolution led to this type of egg, rather than the classic white ones? At first glance it doesn’t make sense, because the blue colour makes the eggs stand out more by exposing them to predators, so it should be a “looser” feature in the evolution race.
A group of researchers decided to study the issue, believing that the bright colour of the eggs should have a functional benefit, which justifies such an evolution. In the end they came to a very interesting conclusion: the colour optimises the amount of light absorbed by the egg, but prevents it from overheating.
According to the research, colour is a balance between two possible negative effects of solar radiation: transmittance through the shell and overheating by absorption. The threats of sunlight are in fact many: the ultraviolet rays could cross the shell and hit the embryo, while the infrared rays can heat the contents of the egg.
More intense and dark colours can act as a “parasol” effect, but at the same time they risk absorbing too much light (the “dark machine” effect, as highlighted by the researchers). Here, then, that evolution has led to a balance between the two needs, necessary in cases where nests are made in places exposed to light, and the colour thus depends on the specific needs of the embryo.